-module(first).
-export([double/1,
         treble/1,
         mult/2,
         square/1,
         area/3]).


mult(X,Y) ->
    X*Y.


double(X) ->
    mult(2,X).


treble(X) ->
    mult(3,X).


area(A,B,C) ->
    S = (A+B+C)/2,
    math:sqrt(S*(S-A)*(S-B)*(S-C)).


square(X) ->
    mult(X, X).
